Magmatic evolution of the South Shetland Islands, Antarctica, and implications for continental crust formation.

Haase, K., Beier, C., Fretzdorff, Susanne, Smellie, J. L. and Garbe-Schönberg, C.-Dieter (2012) Magmatic evolution of the South Shetland Islands, Antarctica, and implications for continental crust formation. Contributions to Mineralogy and Petrology, 163 (6). pp. 1103-1119.

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Abstract

Lavas from the South Shetland Islands volcanic arc (northern Antarctic Peninsula) have been investigated in order to determine the age, petrogenesis and compositional evolution of a long-lived volcanic arc constructed on 32-km-thick crust, a thickness comparable with average continental crust. New Ar-40-Ar-39 ages for the volcanism range between 135 and 47 Ma and, together with published younger ages, confirm a broad geographical trend of decreasing ages for the volcanism from southwest to northeast. The migration pattern breaks down in Palaeogene time, with Eocene magmatism present on both Livingston and King George islands, which may be due to a change in both subduction direction and velocity after c. 60 Ma. The lavas range from tholeiitic to calc-alkaline, but there is no systematic change with age or geographic location. The compositions of lavas from the north-eastern islands indicate magma generation in a depleted mantle wedge with relatively low Sr and high Nd isotopic compositions and low U/Nb, Th/Nd and Ba/Nb ratios that was metasomatized by hydrous fluids from subducted basaltic oceanic crust. Lavas from the south-western islands show an additional sedimentary influence most likely due to fluid release from subducted sediments into the mantle wedge. Although magmatic activity in the South Shetland arc extended over c. 100 m.y., there is no evolution towards more enriched or evolved magmas with time. Few South Shetland arc lavas are sufficiently enriched with incompatible elements to provide a potential protolith for the generation of average continental crust. We conclude that even long-established subduction zones with magmatic systems founded on relatively thick crust do not necessarily form continental crustal building blocks. They probably represent only the juvenile stages of continental crust formation, and additional re-working, for example during subsequent arc-continental margin collision, is required before they can evolve into average continental crust.

Document Type: Article
Additional Information: Haase, KM Univ Erlangen Nurnberg, GeoZentrum Nordbayern, Schlossgarten 5, D-91054 Erlangen, Germany Univ Erlangen Nurnberg, GeoZentrum Nordbayern, Schlossgarten 5, D-91054 Erlangen, Germany Univ Erlangen Nurnberg, GeoZentrum Nordbayern, D-91054 Erlangen, Germany Univ Kiel, Inst Geowissensch, D-24118 Kiel, Germany Univ Leicester, Dept Geol, Leicester LE1 7RH, Leics, England
Keywords: subduction zone magmatism geochemistry fractionation king-george-island back-arc basin subduction-zone fluids geochemical constraints trace-element volcanic-rocks calc-alkaline upper-mantle k-ar livingston-island
Research affiliation: Kiel University > Kiel Marine Science
OceanRep > The Future Ocean - Cluster of Excellence
Kiel University
Refereed: Yes
ISSN: 0010-7999
Projects: Future Ocean
Date Deposited: 14 May 2014 10:05
Last Modified: 11 Apr 2018 11:59
URI: http://oceanrep.geomar.de/id/eprint/24006

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